HSDPA mode of operation, where the users utilize shared network resources, allows mobile devices to receive data at a higher rate than what is achievable utilizing dedicated channels (DCH) in Universal Mobile Telecommunications Service (UMTS) systems. This higher data rate is achieved, in part, by buffering and re-transmitting (if needed) data intended for a mobile device at a Node B of the serving cell, which is physically closer to the end user. Conversely, in dedicated channel mode of operation in a legacy network such as R99 (Frequency Division Duplexing [FDD] systems such as Wideband Code Division Multiple Access [WCDMA]) or R4 (Time Division Duplexing [TDD] systems such as Time Division Synchronous Code Division Multiple Access [TD-SCDMA]), the buffering of data intended for a mobile device is performed at the Radio Network Controller (RNC).
While HSDPA reduces latency and improves throughput performance by moving data re-transmission operations at the Node-B closer to the mobile user, the buffering of data at the Node B causes data loss during handover operations involving serving HSDPA cell change. Specifically, as a mobile device switches from a serving Node B (source) to another (target) Node-B, any data buffered at the source Node B is lost, and must be re-transmitted from the RNC to the target Node B. Moreover, hybrid automatic repeat request (HARQ) entities at the source Node B are deleted, and re-established at the target Node B. In HSDPA mode of operation the cell providing HSDPA services is called the “serving HSDPA cell”. HSDPA operation does not support soft-handover where the UE receives data from multiple cells simultaneously. Therefore at any one time, there is only one serving HSDPA cell for a given UE. When the network sees the need to change the serving HSDPA cell (taking into account UE measurements of neighbouring and serving cells), the network has to cease and delete all HSDPA related parameters (buffers, HARQ queues) at the source cell and move these entities to the target HSDPA serving cell if it wants to continue HSDPA mode of operation.
These issues can increase latency and decrease throughput performance significantly, and particularly when a mobile device performs frequent handovers of the serving HSDPA cell, such as a mobile device moving at high speed, or a mobile device roaming around Node B boundaries.